Vehicle fuel systems include evaporative emission control systems designed to reduce the release of fuel vapors to the atmosphere. For example, vaporized hydrocarbons (HCs) from a fuel tank may be stored in a fuel vapor canister packed with an adsorbent which adsorbs and stores the vapors. At a later time, when the engine is in operation, the evaporative emission control system may allow the vapors to be purged into an engine intake manifold for use as fuel.
The purging of fuel vapors from the fuel vapor canister may involve opening a canister purge valve coupled to a conduit between the fuel vapor canister and the intake manifold. During a purge operation, vacuum or negative pressure in the intake manifold may draw air through the fuel vapor canister enabling desorption of fuel vapors from the canister. These desorbed fuel vapors may flow through the canister purge valve into the intake manifold. As such, the canister purge valve may regulate the flow of fuel vapors into the intake manifold via a sonic choke positioned between a valve in the canister purge valve and the intake manifold. Accordingly, the sonic choke may function as a flow restrictor in the purge path between the valve and the intake manifold.
In boosted engines, during boost conditions when the compressor is operational, the intake manifold may have a positive pressure. Herein, an aspirator coupled in a compressor bypass passage may generate vacuum that can be used to draw stored fuel vapors from the fuel vapor canister via the canister purge valve. However, purge flow through the aspirator may be lower because the sonic choke in the canister purge valve may excessively restrict purge flow to a suction port of the aspirator. Accordingly, a performance of the aspirator in terms of purging the fuel vapor canister may be severely diminished by the presence of the sonic choke in the flow path.
The inventors herein have recognized the above issue and identified approaches to at least partly address the issue. In one example, a method for a boosted engine comprises during boosted conditions, adjusting an opening of a shut-off valve to regulate compressor bypass flow through an aspirator, drawing vacuum at the aspirator, and applying the vacuum downstream of a valve and upstream of a sonic choke, the valve and the sonic choke positioned within a common housing in a canister purge valve. In this manner, the sonic choke may not restrict purge flow to the aspirator.
For example, a canister purge valve comprising a valve and a sonic choke may be included in a boosted engine. The valve may be a solenoid valve. Further, the sonic choke may be positioned downstream of, and proximate to, the valve in the canister purge valve within a single, common housing. The canister purge valve may comprise three ports: an inlet port fluidically coupled to a fuel vapor canister, a first outlet port fluidically coupled from downstream of the sonic choke to an intake manifold, and a second outlet port fluidically coupled from downstream of the solenoid valve and upstream of the sonic choke to a suction port of an ejector. The ejector may be coupled in a compressor bypass passage such that a motive inlet of the ejector is fluidically connected to an intake passage downstream of a compressor, and a motive outlet of the ejector is fluidically coupled to the intake passage upstream of the compressor. Motive flow through the ejector may be controlled by a shut-off valve coupled to the compressor bypass passage upstream of the motive inlet of the ejector. During boosted conditions, the shut-off valve may be adjusted to a mostly open (or fully open) position and the ejector may generate vacuum due to the flow of compressed air in the compressor bypass passage. This ejector vacuum may be applied to the canister purge valve via the second outlet port to draw stored vapors from a fuel vapor canister. Since the ejector vacuum is applied upstream of the sonic choke in the canister purge valve, vapors flowing through the valve in the canister purge valve may bypass the sonic choke as they flow towards the suction port of the ejector. Accordingly, purge flow of fuel vapors from the second outlet port of the canister purge valve into the suction port of the ejector may not be controlled by the sonic choke restriction.
In this way, fuel vapors stored in a fuel vapor canister may be purged in an unrestricted manner by using ejector vacuum during boosted conditions in a turbocharged engine. By circumventing the sonic choke in the purge path via the ejector, a purge flow rate to the compressor inlet may be enhanced. As such, the performance of the ejector in drawing stored fuel vapors from the fuel vapor canister may be improved. Overall, vehicle fuel economy and emissions compliance may be improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.